1. Field of the Invention
The present invention relates to a system and method, such as an electron beam exposure system, for shooting an electron beam at a target, such as a master CD or master DVD (Digital Video Disc or Digital Versatile Disc) detachably held on a rotary stage.
2. Description of Related Art
In a conventional electron beam irradiation system, such as an electron beam exposure system, a target is placed within a vacuum chamber. Under this condition, an electron beam is directed at the target. Where the method involving placing the target within a vacuum chamber in this way is adopted, the structure for replacing the target within the vacuum chamber is complex. In addition, the operation to replace the target is cumbersome to perform.
An electron beam irradiation system fitted with a mechanism that achieves easy replacement of the target is described, for example, in Japanese Patent Laid-Open No. 89922/1985 (JP60089922). In this known system, the inside of the microscope column of electron optics is evacuated to permit an electron beam emitted from the microscope column to be directed at the target without being hindered by the atmosphere. A pumping block is mounted at the lower end of the column and used to evacuate the gap between the column and the target. With the system described in FIG. 3 of this laid-open patent publication, the portion of the target irradiated with an electron beam can be evacuated to a high vacuum of about 10xe2x88x926 torr by drawing in the air from the gap. Furthermore, with the system illustrated in FIG. 4 of this laid-open patent publication, the gap can be evacuated to a vacuum of about 10xe2x88x922 torr by making use of a negative pressure (Bernoulli Effect) created by air drawn out of the outer periphery of the gap.
With the aforementioned electron beam irradiation system, the target is detachably held on an XY stage. The position of the target is adjusted by driving the XY stage vertically and horizontally. When the target is mounted on or removed from the XY stage, it is driven to move the target into a position lying outside the pumping block of the microscope column of electron optics. At this time, one end of the XY stage is located immediately under the pumping block. This prevents the degree of vacuum from deteriorating. If the portion of the XY stage located immediately under the pumping block (i.e., the portion of the XY stage extending outwardly from the target) is too distant from the pumping block, the vacuum will deteriorate when the target is mounted or removed. If this occurs, it takes a long time to again sufficiently evacuate the inside of the microscope column containing the electron optics.
A target, such as a master CD or master DVD, that is a substantially circular storage medium is mounted on a rotary stage instead of the XY stage described above. In an electron beam irradiation system fitted with such a rotary stage, the target and rotary stage are conventionally placed within a vacuum chamber and a pumping block is not placed at the end of the microscope column.
An electron beam irradiation system fitted with the rotary stage and having the pumping block mounted at the end of the electron optical microscope column is discussed further below. The end portion of the stage on which the target is placed extends outwardly from the target to prevent vacuum deterioration as mentioned previously. Where the stage is an XY stage, if the end portion were at one end of the XY stage, then satisfactory results would arise. Where the stage is a rotary stage, the end portion needs to exist along the whole outer periphery of the rotary stage. This makes the whole rotary stage very bulky. Furthermore, where the end portion protruding out of the target is made larger to prevent vacuum deterioration more effectively, the rotary stage will be made very large. This, in turn, increases the driving force necessary to rotate the stage. Additionally, the rotation may not be stably controlled.
It is an object of the present invention to provide an electron beam irradiation system which is fitted with a rotary stage and has a pumping block placed at an end of a microscope column of electron optics, the system being characterized in that vacuum deterioration can be prevented during mounting and removal of a target without increasing the size of the rotary stage.
An electron beam irradiation system according to the present invention comprises: a rotary stage capable of detachably holding a target thereon; an electron optical microscope column for directing an electron beam at the target held on the rotary stage; a pumping block mounted at an end of the electron optical microscope column to evacuate air in the gap between the microscope column and the target; a moving mechanism for sliding the rotary stage relative to the microscope column radially of the rotary stage between a working position where the target held on the rotary stage is opposite to the microscope column and a mounting position where the target held on the rotary stage is spaced from the microscope column; and a cover member. When the rotary stage moves from the working position to the mounting position, the cover member is brought close to or into intimate contact with either a side surface of the rotary stage or a side surface of the target to prevent vacuum deterioration. When the rotary stage is in the mounting position, the cover member is opposite to the microscope column.
When the rotary stage rotates, a gap is formed between one of the side surface of the rotary stage and the side surface of the target on the rotary stage and the cover member. When the rotary stage moves from the working position to the mounting position, the cover member can move relative to the rotary stage or the target on the stage to thereby remove the gap.
When the electron beam is directed at the target held on the rotary stage from the electron optical microscope column, the pumping block evacuates the air in the gap between the microscope column and the target. The rotary stage is moved radially by the moving mechanism while rotating the stage when the microscope column is located opposite to the target. After irradiation, the target is replaced. At this time, the rotary stage is moved from the working position to the mounting position while continuing the pumping operation using the pumping block. In this mounting position, the target is replaced. The rotary stage is moved from the mounting position to the working position by the moving mechanism. During movement of the rotary stage between the working position and the mounting position, the microscope column is placed opposite to the target, rotary stage, or cover member. The stage is not exposed to the atmosphere and so vacuum deterioration can be prevented.
When the rotary stage turns, the cover member is moved away from the rotary stage or the target to form a gap between one of the side surface of the rotary stage and the side surface of the target and the cover member. During movement of the rotary stage between the working position and the mounting position, the cover member is moved toward the rotary stage or target, thus bringing the cover member into intimate contact with the side surface either of the rotary stage or of the target.
Other objects and features of the invention will appear in the course of the description thereof, which follows.